Fuel vapor canisters are utilized in fuel systems to capture fuel vapors that arise within the fuel tank. Specifically, a first conduit may couple the fuel tank to the fuel vapor canister to allow for a migration of fuel vapors away from the fuel tank. These canisters are filled with an adsorbent such as activated carbon so as to trap the fuel vapors within the canister. A second conduit coupling the canister to an engine intake and a third conduit coupling the canister to a fresh air source allows for the trapped fuel vapors to be recycled into the combustion chambers while loading fresh air onto the adsorbent. The second conduit includes a canister purge valve for allowing vapors to escape the canister via the manifold vacuum during select conditions. One condition during which it is desirable to purge the fuel vapor canister is when the adsorbent reaches a percentage of full saturation or full saturation.
A temperature sensor may be included within the fuel vapor canister to determine the saturation level of a canister. Specifically, it is well known in the art that the temperature within the vapor canister increases as the loading state (e.g., the amount of fuel vapor deposited on the adsorbent therein) increases. Similarly, as a canister is purged, the temperature decreases and may reach a stable base temperature as the amount of fuel vapor within the canister approaches zero. Thus, a loading state may be estimated based on a temperature signal from a sensor within the vapor canister.
However, vapor adsorption rates may not be uniform within a fuel vapor canister, at least for the reasons of uneven airflow within the canister and the relative positioning of the aforementioned conduits. Thus, an estimate of loading state based on a single temperature sensor may be inaccurate due to a limited sensing range within the canister. For example, if the temperature sensor is placed at a location where vapor is adsorbed more rapidly, the temperature may indicate a fully saturated canister when other areas despite other areas in the canister being only partially saturated.
Other attempts to address managing adsorption levels within a fuel vapor canister include utilizing a plurality of temperature sensors along the canister flow path to determine adsorption at various points therein. One example approach is shown by Veinotte in U.S. Pat. No. 7,233,845. Therein, a fuel vapor canister includes a plurality of temperature sensors are installed along a flow path of the canister to determine adsorption levels at a plurality of locations along the flow path.
However, the inventors herein have recognized potential issues with such systems. As one example, due to the curved flow path of the canister, the temperature sensors must be disposed at carefully measured lengths within the adsorbent in order to measure different locations along the adsorption front, thereby introducing an undesirable degree of complexity to the manufacturing process. Additionally, due to the inclusion of each of the temperature sensors on a common printed circuit board and common electrical lead, maintenance costs of the plurality of temperature sensors of the canister of Veinotte may be high. Specifically, degradation of a single temperature sensor may require replacing each of the temperature sensors rather than only the degraded sensor.
Thus, the inventors herein have developed systems and methods to at least partially address the above issues. In one example a method is provided, comprising adsorbing fuel vapors or desorbing fuel vapors in a plurality of individual vapor storage modules which are coupled to a vehicle fuel tank; monitoring a plurality of temperature sensors each coupled to one of the individual modules; and indicating that one or more of the individual modules are not functioning as desired responsive to a monitored temperature change being different than an expected temperature change during the adsorbing or desorbing of fuel vapors.
As one example, prior to the adsorbing or desorbing of fuel vapors in the individual vapor storage modules, a loading state of each individual module is recorded, where the loading state includes an indication of a fuel vapor saturation level within each individual module. With the loading state of each individual module recorded, the expected temperature change is based on the loading state, and is further based on an expected amount of fuel vapors adsorbed or desorbed by individual modules during the adsorbing or desorbing. In some examples, adsorbing fuel vapors in the individual vapor storage modules occurs during refueling of the vehicle fuel tank, where fuel vapors generated during the refueling are directed to the individual vapor storage modules for adsorption, and wherein adsorbing fuel vapors results in a temperature increase in one or more of the plurality of individual vapor storage modules. Furthermore, in some examples, desorbing fuel vapors in the individual vapor storage modules occurs during a purge event, where the purge event further comprises coupling the individual vapor storage modules to an engine intake manifold and to atmosphere to draw fresh air across the individual vapor storage modules such that stored fuel vapors are desorbed and routed to the engine intake manifold for combustion, and wherein desorbing fuel vapors results in a temperature decrease in one or more of the plurality of individual vapor storage modules. In this way during a refueling event, or during a purging event, individual canister modules within a modular fuel vapor canister may be reliably assessed as to whether each individual canister module is functioning as desired. By enabling an ability to diagnose the functionality of individual modules, in a case where it is determined that one or more modules are not functioning as desired, only the modules that are not functioning as desired may be serviced and/or replaced, which may thus reduce overall servicing costs and replacement costs.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.